1. Field of the Invention
The present invention relates generally to a screen for displaying, on an enlarged scale, an image projected by a projector or a projection TV set and in particular but not exclusively to a portable screen assembly that is easy to carry and can be installed at an optional location such as, for example, on a floor, a table or the like.
2. Description of the Prior Art
An image projected by a projector or, in some cases, a projection TV set is generally displayed, on an enlarged scale, on a reflection type screen or on a transmission type screen.
Of such screens, some are generally accommodated in a housing mounted on a ceiling or a side wall, and are electrically or manually extended as the occasion demands. Hanging screens or screens with a tripod are used by hanging or locating them at a desired place.
Portable screen assemblies are today available in which a screen is wound around a roll housed in a housing. When such screen assemblies are in use, the housing is initially installed at a desired place, and the screen is subsequently extended by, for example, an extension means somewhat similar to a pantograph by the action of the biasing force of a spring mounted therein.
Recently, the number of meetings or conferences has increased in companies or offices and there is an increasing demand for a portable screen assembly having a simple structure that is easy to carry with a projector and can be installed on a floor, a desk or a table in a conference room to display an image projected by the projector.
Further, there is a problem with the conventional pantograph that the pantograph is hard to get balanced laterally (i.e., in right and left symmetry) when it is lifted, and this tends to cause the top bar to tilt. As a result, the screen is wound around the spring-biased roll in a bamboo-like fashion, thus tending to cause the trouble of damaging the screen.
Another problem is that where arms of the pantograph and the spring-biased roll are mounted in an axially misaligned condition, the spring-biased roll and the top bar are not in axially parallel alignment when the screen is stretched and this causes the screen to distort. However, high precision is required to eliminate the possibility of such a problem of distortion when mounting the constituent parts to the pantograph and the pantograph to the lower casing, which results in a high cost of fabrication.